A major portion of the worldwide petrochemical industry is concerned with the production of light olefin materials and their subsequent use in the production of numerous important chemical products via polymerization, oligomerization, alkylation and other well-known chemical reactions. Light olefins include ethylene, propylene and mixtures thereof. These light olefins are essential building blocks for the modern petrochemical and chemical industries.
Olefin conversion technologies may be employed to produce light olefins from other olefins. Such olefin conversion processes are often combined or integrated with other olefin producing technologies such as, for example, steam or fluid catalytic cracking processes or oxygenate to olefin processes to provide increased light olefin production.
There are generally two main types of olefin conversion technologies available to produce light olefins, metathesis and olefin cracking. Such metathesis processes typically produce propylene by reacting ethylene with 2-butenes. Such olefin cracking processes typically produce ethylene and propylene by cracking or converting C4-C8 feedstocks to produce effluent streams containing predominantly C2-C6 compounds along with some hydrogen and other lighter gases. Such effluent streams are subsequently separated into various product streams such as, for example, product streams containing ethylene and propylene.
While such processing can desirably result in the formation of increased relative amounts of propylene and/or ethylene, further improvements such as to further enhance the relative amount of propylene and/or ethylene production and recovery are desired and have been sought.
Generally, olefin cracking processes are conducted in a reactor at elevated temperatures and typically produce effluent streams having temperatures in excess of 500° C. Such olefin cracking reactor effluent streams are subsequently cooled and compressed to facilitate separation into individual product streams. Olefin cracking reactor effluent streams can be cooled using various heat exchange methods such as, for example, indirect heat exchange with a cooling medium such as, for example, cooling water. One such indirect heat exchange method generally involves passing the hot olefin cracking reactor effluent through a heat exchange unit such as, for example, a tube and shell heat exchanger, to produce a cooled olefin cracking reactor effluent stream having a temperature profile that is suitable for efficient compression.
However, such indirect heat exchange units can be susceptible to fouling by constituents of the olefin cracking reactor effluent stream. For example, heavy hydrocarbon compounds can condense on surfaces of the heat exchange unit which can result in a reduction of the cooling capacity of the heat exchange unit. Generally, the temperature of a gas to be compressed controls the capacity of an associated compressor, i.e., the higher the temperature of the gas the less it can be compressed. Thus, reducing the cooling capacity of the heat exchange unit results in a reduced compression capacity in an associated compressor which can, in turn, result in increased down time for cleaning of the heat exchange units and decreased product output.
In view of the above, there is a need and a demand for processing schemes and/or arrangements effective to reduce fouling of heat exchange units used to cool olefin cracking reactor effluent streams.
Additionally, gaseous materials which pass through such indirect heat exchange units can also experience a significant pressure drop from inlet to outlet resulting in a cooled effluent stream having a pressure which is lower than may be desired and can require additional energy expenditures and increased compressor size to compress the cooled effluent stream to a pressure suitable for further processing in subsequent separation units. Thus, there is a further need and a demand for processing schemes and/or arrangements that result in a reduced pressure drop across the heat exchange unit.
Further, a pressure drop across the heat exchange unit can result in an increased pressure at an associated olefin cracking reactor outlet which can cause reductions in the yield of ethylene and/or propylene produced by the olefin cracking process. Accordingly, there is a still further need and a demand for processing schemes and/or arrangements effective to result in an increased relative yield of light olefins, particularly, ethylene and/or propylene.